During military, police or emergency services training exercises respirator masks are deployed so that personnel can become familiar with the equipment that they will need to protect them from toxic substances in the air.
Gas attack simulation systems exist that utilise a simulator filter in place of the normal filter in a gas mask. Breathing activity may be monitored by the system to determine whether the mask is being worn and a particular user can be designated wounded or killed in the event they do not use the device.
For example, a prior art respirator training systems are described by US2007/0017509 (EMRICSON et al) and CH 692103 A5 (LAZECKI) which rely upon the detection/sensing capability of the training filter to determine a correct fit of the respirator mask. In the case of a noxious substance being reported present in the training exercise, but the respirator is either not being worn or worn correctly, the control system records the individual as dead or incapacitated as appropriate.
US2011/0277759 (CRUTCHFIELD) describes a respirator fit-test method by a combination of an air flow monitor and pressure monitor, however, this is specifically for determining correct fit (i.e. no leaks) and not for wearing as a training aid.
In training situations the type of filter being simulated is, for example, an activated carbon filter which is used in personnel respirators (generally referred to as a canister(s)), vehicle filters and filters for air systems in temporary or permanent buildings. The filtration mechanism may be by adsorption, where the pollutant attaches itself to the activated carbon; and absorption, where the pollutant is absorbed by the activated carbon.
Such filters have a finite capacity to protect in that when the filter layer has been saturated, the noxious substance will then generally pass straight through or, alternatively, the filter layer will become clogged making breathing increasingly difficult for the user downstream of the filter.
For example, some hazardous substances are known to be such that a typical activated carbon respirator filter will only provide 15 minutes protection, rather than the 8 hours that might be expected against more general chemical warfare substances. Particularly, filters designed to provide protection against chemical warfare substances do not generally provide protection against toxic industrial substances.
Some filters have a means of indicating their “end of life” but many do not. An end of life service indicator (ELSI) is a device that is incorporated within a respirator canister to provide a visual indication to the wearer of the remaining service life of a canister. Such technology is in early development and the ideal solution is very much sought after. Some basic ELSIs exist and are in use by various Governments.
In the majority of circumstances, where no “end of life” indicator means is available, the practice is to replace the filter after a prescribed number of hours use. It is however the responsibility of the wearer to decide what constitutes an appropriate number of hours of use, and also to ensure the required number of spare respirator canisters are available.
The prior art (e.g. US2007/0017509) does not address the fact that the filter may not offer adequate protection in a given scenario or that a filter may have “expired” after prolonged use, even if the respirator is correctly worn and the simulation canister correctly fitted. The prior art also tends to be specific to respirators as worn by a human and are not intended for wider applications.